Magnetic materials and process of preparation



Feb. 27, 1968 M. w. SHAFER 3,370,916

MAGNETIC MATERIALS AND PROCESS OF PREPARATION Filed June 27, 1963 INVENTOR. MERRILL W. SHAFER ATTO RNEY

United States Patent 3,370,916 MAGNETIC MATERKALS AND PROQESS 0F PREPARATEGN Merrill W. Shafer, Yorktown Heights, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed June 27, 1963, Ser. No. 291,043 6 Claims. (Cl. 2321) ABSTRACT OF THE DISCLOSURE A method for forming a group of europium silicate magnetic materials the members of which have unpaired electrons and are transparent in relatively thick layers at wavelengths greater than about 4500 A. in which intimate mixtures of EuO or EuCO or Eu(OH) and Si0 are reacted at elevated temperatures in a non-oxidizing or insert gas environment. Other europium compounds such as Eu (C O Eu(OH) or Eu O may be mixed with SiO and reacted at elevated temperatures in a reducing atmosphere to provide the same europium silicate group. The compositions resulting from the process are europium silicates having the formula Eu SiO where x: 1-3.

Magnetic materials generally fall into two classes, those which exhibit cooperative magnetism, and those which do not. Those with the cooperative magnetic effect are the ferromagnetic, ferrimagnetic and anti-ferromagnetic materials. The great majority of the ferromagnetic materials are metals and good electrical conductors, hence, opaque materials. The ferrimagnetic materials can have a range of restivities, but their conduction bands are partially filled and also are opaque for all practical purposes. Although the antiferromagnetic materials can have unfilled conduction bands, their net magnetic moments are small and consequently have little practical use.

The existence of insulating ferromagnetic or ferrimagnetic materials is rare since they would require that the conduction band be unfilled and still exhibit a positive interaction involving unpaired electrons. Examples of these materials would be CrBr and Na Fe P On the other hand, the yttrium iron garnets, e.g., Y Fe O and rare earth iron garnets only partially fill these requirements since they are only transparent in very thin sections.

It is well known that when a light is passed through a magnetic material in which there are unpaired electrons, there Will be an interaction and the light will be rotated in a manner which is dependent on the alignment and the number of unpaired electron spins of the material (i.e., the Faraday effect). This Faraday effect is usually defined in terms of the Verdets constant which is the observed rotation in minutes per gau'ss per centimeter thickness.

This is also true in the case of paramagnetic materials as well as in the case of ferromagnetic and ferrimagnetic materials. Thus, the greater the number of unpaired electrons and their ability to align in a magnetic field, the greater will be the specific rotation of the light that the material can transmit (i.e., the specific rotation is directly proportional to the magnetic susceptibility of the material).

A group of europium silicate magnetic materials has been prepared, the members of which have unpaired electrons and are transparent in relatively thick layers in the visible and near visible spectrum (i.e., wavelengths greater than about 4500 A.). These materials have the formula Eu SiO Where x: 1-3. Those europium silicates where x=2 or 3 exhibit a high saturation magnetization. The europium silicate where x=l is paramagnetic. All the europium silicates are chemically stable under ordinary conditions and optically transparent in single crystal form.

It is an object of the invention to prepare europium silicate magnetic materials.

It is a further object of the invention to prepare europium silicate magnetic materials having the formula Eu SiO J where x=13 and which are transparent.

Another object of the invention is to prepare a paramagnetic material having the fonmula EuSiO Still another object of the invention is to prepare a ferromagnetic material having the formula Eu SiO A still further object of the invention is to prepare a ferromagnetic material having the formula Eu SiO Further, another object of the invention is a magnetooptical device utilizing a crystal of Eu SiO where x: l-3.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawing.

The drawing is a diagrammatic showing of a magnetooptical device utilizing a europium silicate crystal of the present invention.

In the magneto-optical device shown diagrammatically in the drawing, a single crystal (or crystal section) 1 of a ferroor paramagnetic europium silicate of the present invention is mounted between spaced crossed polarizing filters (i.e., polarizer 2 and analyzer 3). The crystal is placed in a magnetic field (e.g., that produced by an electromagnet 4 or by Helmholtz coils). A light source 5 and a photosensitive cell 6 are so disposed that the light to which the photosensitive cell is exposed is that which originates at the light source and passes successively through polarizer 2, crystal 1 and analyzer 3. Since the degree of rotation of the plane of polarized light passing through the paramagnetic crystal is dependent upon the magnetic field, the amount and orientation of light originating in the light source and passing through the polarizer and analyzer and crystal to the photosensitive cell can be varied by varying the strength of the magnetic field of the magnet. In the ferromagnetic region, above magnetic saturation, the rotation is independent of the applied magnetic field and the maximum rotation can be obtained.

All these europium silicate materials have high Verdets constants even at room temperature because of their high magnetic susceptibility and high degree of transparency. This Verdets constant is higher by a factor of about 10 than that of any previously-known material. As a result of this high Verdets constant, all these europium silicate materials can be used in magneto-optical devices such as laser beam modulators, light switches, etc. The compounds Eu SiO and Eu SiO exhibit a very large Faraday rotation at helium temperature. In addition, the new ferromagnetic materials, which are insulators, have properties which find application in memory elements, transformer cores,

or in any device Where high magnetic susceptibility material is desired at low temperatures.

Table I gives the magnetization data showing magnetic 3 susceptibility versus temperature in degree Kelvin for the three europium silicates. The saturation magnetization and Curie temperature data are shown in the right column. All measurements were made using standard techniques.

TABLE 1 Temp. Magnetic I K.) Susceptibility Magnetic Saturation Properties EuSiO 262 126 Paramagnetic to 1.8 K. consequently no 194.5 176 saturation magnetization or Curie ttni- 167. 3 207 perature measurements could be made. 107. 7 311 258.5 136 Ferromagnetic saturation magnetization 236.7 152 6.54 Bohr Magnetrons or 185 emu/gm. 200. 3 172 Curie temperature 10 LL. 179.5 201 En SiOs 270 140 Ferromagnetic saturation magnetization 241 157 6.10 Bohr Magnetrons or 175 emu/gm. 194. 5 195 Curie temperature 4 K. 9 180.3 200 All the europium silicates of the invention exhibit magneto-optical and optical properties. In Table IT below, these properties are set forth for Eu SiO All measurements were made at room temperature using standard techniques.

Verdet constant at 25 C.=2.5 min./oe./cm.i%.

The Eu SiO (where x=13) magnetic materials are prepared by reacting intimate mixtures of EuO or EuCO or Eu(OH) and SiO at elevated temperatures between 800-1600 C. under nonoxidizing conditions such as an oxygen free vacuum or any condition in which there is an absence of oxygen, such as argon, nitrogen, etc., or under reducing atmosphere containing large percentages of hydrogen, e.g., nitrogen with hydrogen added (1-100 percent hydrogen), CO with approximately -80 percent hydrogen, argon containing l-lOO percent hydrogen and pure hydrogen. Alternately, these materials can be prepared by reacting either Eu (C O Eu(OH) or Eu O with SiO in a pure hydrogen atmosphere at temperatures between 15002000 S. The crucible used in preparing these materials is composed of iridium, platinum, or carbon.

The following specific examples represent embodiments of the invention and, more particularly, disclose the preparation of the europium silicate magnetic materials.

4 Example I (Eu SiO 33.6 grams of EuO are intimately mixed with 6.0 grams of SiO This mixture is then placed in an iridium crucible. The crucible was raised to a temperature greater than 800 C. in a pure hydrogen atmosphere and held at that temperature for 24 hours. The crucible was then cooled to room temperature at a rate of 50 C. per minute. The resultant product Eu SiO is a lemon-yellow polycrystalline powder Jlth a Curie temperature of 10 K.

Example I! (EuSiO 16.8 grams of EuO are intimately mixed with 6.0 grams of SiO This mixture is then placed in a platinum crucible. The crucible is placed in an oven and the temperature is raised to 1200 C. in a pure argon atmosphere and held at that temperature for 15 hours. The crucible was then cooled to room temperature at a rate of 50 C. per minute. The resultant product EuSiO is a lemon-yellow powder which is paramagnetic down to 136 K.

Example 111 (Eu SiO 50.4 grams of EuO and 6.0 grams of SiO are intimately mixed with 6.0 grams of SiO This mixture is placed in a carbon crucible and the crucible is placed in an oven. The temperature was raised to 1600 C. in a pure nitrogen atmosphere and held at that temperature for 12 hours. The resultant product Eu SiO is .a powder with a lemonyellow color and a Curie temperature of 4 K.

Example IV (EU2SlO4) 35.2 grams of Eu O are intimately mixed with 6.0 grams of S10 and placed in a carbon crucible. The crucible is laced in an oven and the temperature raised to 1600 C. in a pure hydrogen atmosphere and held at that temperature for 36 hours. The crucible is then cooled to room temperature at a rate of 10 C. per minute. The resultant product are amber-colored crystallites, some of which are large enough that optical and magneto-optical measurements may be made thereon.

The devices of the present invention have been described as made up essentially of a crystal containing Eu SiO which is placed in a magnetic field and associated optical instrumentation in order to utilize the Faraday effect. These devices may be manufactured according to the technique known in the art for the manufacture of analogous devices embodying other crystal bodies. The best results are obtained when the specific rotation of the light passing through the crystal varies linearly with the applied magnetic field.

However, the maximum rotation obtainable for this material can be obtained when operated in the ferromagnetic state, i.e., below their Curie temperature 10 K. for Eu SiO and 4 K. for Eu SiO The new europium silicates of the invention have the formula Eu SiO where x=l-3. These silicates are transparent and thus are used in magneto-optical devices.

While the invention has been particularly shown and described with reference to a preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1.1 1; compound having the formula Eu SiO where x:

2. The compound EuSiO 3. The compound Eu SiO 4. The compound Eu SiO 5. A process of preparing an europium silicate material having the formula Eu SiO Where x=13 Which comprises the steps of:

(a) intimately mixing S10 with an europium compound selected from the group consisting of EuO, EuCO and Eu(OH) (b) heating this mixture in a nonoxidizing atmosphere at elevated temperatures between 800-1600 C. to form thereby the europium silicate and then cooling.

6. A process of preparing an europium silicate material having the formula Eu SiO Where x=13 which comprises the steps of:

(a) intimately mixing Si0 with an europium compound selected from the group consisting of 1311 0 Eu(OH) and Eu (C O (b) heating this mixture in a hydrogen atmosphere at temperatures between 1500-2000 C. to form thereby the europium silicate and then cooling.

6 References Cited UNITED STATES PATENTS 11/1964 Geller 350160 X OTHER REFERENCES EDWARD J. MEROS, Primary Examiner.

OSCAR R. VERTIZ, JEWELL H. PEDERSEN,

Examiners.

A. GREIF, P. R. MILLER, Assistant Examiners. 

